Questions about how best to place students into appropriate middle grade math courses have been central to ongoing education policy and practice discussions in California and across the United States. Recent studies have shown that enrolling in algebra I in grade 8 works well for some students but backfires for others. This REL West report provides findings from a study of placements that were based on different test scores available for middle school students in California. Findings indicate that placement into grade 8 algebra I based solely on students' grade 6 California Standards Test (CST) proficiency status results in some students taking the course who have less than a 40 percent chance of succeeding. Using a higher cut point on the grade 6 CST scale score--as opposed to simply using CST proficiency status--would avoid placing students into grade 8 algebra I who have a lower than 50 percent chance of success, and would increase the overall success rate (from 69 to 75 percent) for students placed into grade 8 algebra I. Prediction accuracy is even higher using grade 7 CST scale scores (78 percent); however, grade 7 scale scores are typically not available until after initial algebra I placements are made. The study also finds that a newly available assessment of algebra readiness developed as part of the Math Diagnostic Testing Project (MDTP) makes a valuable contribution to decisions about algebra I placement. Placements based on the MDTP result in a success rate (77 percent) that is comparable to that of placements based on the grade 7 math CST. Furthermore, the MDTP test can be administered online at any time during the school year, and MDTP test results are available immediately after students take the test, whereas CST results are not available until the next school year. The following are appended: (1) Detailed study design; and (2) Model comparisons.